The use of fluid heat exchangers is commonplace where heat is to be extracted from a fluid. Single-fluid heat-exchanging systems generally employ a cooling core to extract heat from the fluid. The heat extracted from the fluid is passed, primarily through convection, to the surrounding atmosphere. Conventional automotive radiators and heaters are exemplary of single-fluid heat-exchanging systems. The single fluid to be cooled is typically automotive antifreeze.
In many cases, a second fluid is also to be cooled. Such dual-fluid heat-exchanging systems often employ a thermal-transfer unit to extract heat from the second fluid and pass that heat, primarily through convection and conduction, to the first fluid. The cooling of the first fluid, therefore, provides the cooling of the second fluid. A conventional automotive radiator incorporating an oil cooler is exemplary of such a dual-fluid heat-exchanging system. The first fluid to be cooled is typically automotive antifreeze and the second fluid to be cooled is typically automatic transmission oil, engine oil, or the like.
Numerous problems arise with conventional dual-fluid heat-exchanging systems. To better understand these problems, the operation of a dual-fluid heat-exchanging system will briefly be covered. For purposes of discussion, a dual-fluid automotive heat-exchanging system incorporating a radiator configured to extract heat from an automotive engine by means of a coolant (water or antifreeze), and an oil cooler configured to extract heat from an automotive transmission by means of a transmission oil is presumed.
A typical radiator is made up of an input tank, a cooling core, and an output tank. The input tank serves both as a coolant reservoir and as a manifold configured to route the coolant from the engine to the cooling core. Similarly, the output tank serves both as a coolant reservoir and as a manifold configured to route the coolant from the cooling core back to the engine. The cooling core is made up of a multitude of thin-walled, thermally conductive tubes connected to a multitude of thermally conductive "radiating fins."
In operation, the coolant absorbs heat from the engine. The heated coolant then passes from the engine into the input tank and thence into the cooling core. As the coolant passes through the cooling core, the heat contained in the coolant is conducted through the thin-walled tubes and into the radiating fins. The heat passes thence into the air, where it is dissipated by convection. The cooled coolant then passes from the cooling core into the output tank and thence into the engine, completing the cycle.
A typical radiator-coupled oil cooler is similar in construction and operation. The oil cooler is made up of an input manifold or reservoir, a thermal-transfer core, and an output manifold or reservoir. The thermal-transfer core is made up of thin-walled, thermally conductive tube(s). The core or, often, the entire oil cooler is embedded within one of the radiator tanks, hence is surrounded at all times by the coolant.
In operation, the oil absorbs heat from the automotive transmission. The heated oil then passes from the transmission into the input manifold or reservoir, and thence into the thermal-transfer core. As the oil passes through the thermal-transfer core, the heat contained in the oil is conducted through the thin-walled tube(s) and into the coolant, where it is dissipated by convection. The cooled oil then passes from the thermal-transfer core into the output manifold or reservoir, and thence into the transmission, completing the cycle.
A potential problem exists in the materials from which the various components of the heat-exchanging system are fabricated. For the radiator core, a material such as a cupriferous or aluminiferous metal is preferred. Such metals are easily cast or machined, possess sufficient strength, and exhibit excellent thermal conductivity and transfer characteristics. Components fabricated of cupriferous metals have the additional advantage of being readily assembled through soldering, brazing, etc. However, components fabricated of aluminiferous metals may be clad with a suitable alloy to provide this capability.
The radiator input and/or output tanks, serving as reservoirs and manifolds only, do not share the thermal characteristic requirements of the cooling-core components. The tanks, therefore, need not be fabricated of the same materials nor in the same manner as the cooling core. They therefore may be fabricated of inexpensive metals, plastics, resins, or other materials.
The oil cooler is typically an independent assembly fitted into one of the radiator tanks. It is the task of the oil cooler core to transfer heat from the transmission oil to the coolant. The efficiency of this thermal transfer is a function of two basic factors, the inter-fluid interface area and the thermal conductivity of the material separating the transmission oil from the coolant. The same thermal transfer may be realized by a core having a small inter-fluid interface area and a high thermal conductivity as a core having a large inter-fluid interface area and a low thermal conductivity. In other words, a small oil cooler fabricated of a cupriferous metal may have substantially the same thermal transfer characteristics as a large oil cooler fabricated of resin.
Since different components of a dual-fluid heat-exchanging system have different requirements, dissimilar materials are often used. Wherever dissimilar materials come into contact, an interface problem exists. For example, an aluminiferous metal cooling core may be used with resin input and output tanks and a cupriferous metal oil cooler. The differences in thermal expansion of the differing materials cause a significant thermal stress at inter-material interfaces. This thermal stress in turn creates a potential for leakage. Partial compensation for this thermal stress is conventionally provided by the use of seals, gaskets, etc. These seals, gaskets, etc., are subject to decomposition, vibrational wear, drying out, or other degeneration producing a limited life-span and a significant reduction in the reliability of the heat-exchanging system.
A related problem exists in that the use of seals, gaskets, etc., creates a complex assembly. The fabrication of such an assembly requires multiple operations, resulting in a high fabrication cost.
The fabrication of an oil cooler from plastic or resin, while offering an economy of manufacture, requires that the oil cooler be substantially larger than one fabricated of metal. Since the oil cooler is conventionally embedded within a radiator tank, a plastic or resin oil cooler requires that the radiator tank be significantly larger than otherwise. This presents a problem in scale, wherein a larger-than-otherwise radiator tank implies a larger than otherwise radiator overall, and a less flexible usage, e.g., requires a larger car hood, etc.
Both the thermal-stress and scale problems may be addressed by fabricating all components of substantially the same material, i.e., of a cupriferous or clad aluminiferous metal. In such a case, a problem remains in that conventional manufacturing techniques still dictate the use of seals, gaskets, etc., as described hereinabove. Therefore, the problems of complexity of structure, difficulty of manufacture, and cost of manufacture remain.
What is needed, therefore, is a methodology of manufacturing a dual-fluid heat-exchanging system that eliminates the use of seals, gaskets, etc., between components of the system.
What is needed is a methodology of manufacturing a dual-fluid heat-exchanging system offering a substantial decrease in complexity over conventional methodologies.
What is needed is a dual-fluid heat-exchanging system wherein all major components thereof are fabricated from substantially the same material.
What is needed is a dual-fluid heat-exchanging system wherein that material is a cupriferous metal or an aluminiferous metal.
What is needed is a dual-fluid heat-exchanging system wherein the secondary-exchanger thermal-transfer core presents a significant inter-fluid surface to both the primary and secondary fluid so as to facilitate the transfer of heat from the secondary fluid to the primary fluid.
What is needed is a dual-fluid heat-exchanging system offering a substantial overall reduction in cost over current systems.